1. Field of the Invention
The present invention relates to a physiological sensor device or sensor array for attachment to a mammalian subject in order to obtain data about one or more physiological parameters of the subject. In particular, the invention relates to a physiological in sensor device in the form of a patch attachable to the chest of a human subject to enable sensing of physiological data such as electro-cardiographic data and/or respiration data.
2. Description of the Prior Art
The prior art includes U.S. Pat. No. 3,943,918 to Lewis which discloses an ECG signal sensing and transmitting device for use in the care of medical patients requiring monitoring of cardiac functions. The device disclosed is a single use, disposable unit consisting principally of a foam pad having a pair of circular electrodes in one face of the rectangular foam block. The block comprises electrical circuitry which transmits an RF signal to a receiver which is required to be within 100 feet of the patient. Subsequent filtering and amplification of the signal takes place at a monitoring station comprising a receiver and the like. The device is disposable after one use but, as a result, is somewhat crude and only comprises two electrodes for very basic ECG measurements.
U.S. Pat. No. 4,121,573 discloses a chest sensor for monitoring cardiac rhythms of a patient using a pair of spaced circular electrodes mounted on a foam pad. Electrical connectors between the electrodes and electronic circuitry for acquiring and transmitting cardiac rhythm signals is provided by independent electrical leads or wires. The circuitry and wires are located on the rear surface of a first layer of foam and held in position by a second layer of foam. Accordingly, a fairly deep configuration of layers of foam, electronic circuitry and electrodes is provided in this rather crude two electrode device.
U.S. Pat. No. 4,957,109 discloses an electrode array for use in generating electrocardiographic signals for a patient. The array comprises ten different electrode regions (comprising pairs of semicircular electrodes) for attachment to different parts of the human body. The electrodes are interconnected to an output connector for attachment to signal processing apparatus. The electrode sensors and electrical conductors between the electrodes and the output conductor are formed on a large flexible circuit board having a large dentritic or tree-like configuration to enable location of the electrodes at appropriate positions on the human body for standard twelve lead diagnostic electrocardiogram studies. A digital infra red signal having multiplexed data from each of the ECG electrodes is transmitted to a remote location in use. While fairly sophisticated, this arrangement only contemplates point-in-time 12 lead ECG studies and is not disposable.
U.S. Pat. No. 5,634,468 discloses a sensor for physiological monitoring of a patient, consisting of a rectangular patch having a central structural member formed of MYLAR(trademark) encased in an adhesive hydrogel. One side of the sensor has four circular electrodes for contacting the patient. The electrodes are wired to an electronic package on the opposite side of the structural member. The electronics package is adapted to receive ECG data and transmits the data to a monitoring unit. However, this small sensor is limited to measuring ECG signals.
U.S. Pat. No. 5,353,793 discloses sensor apparatus for making ECG measurements comprising a band which passes entirely round a patient""s chest. The chest band can have optional shoulder straps and an optional abdominal band. Electrodes are positioned around the inner circumferential surface of the band for monitoring respiration, pulse and ECG signals. The ECG electrodes are simple conductive sensors in electrical contact with the skin. The pulse and respiration sensor comprises a tension sensor consisting of a piezoelectric element A minimum of 7 ECG sensors is provided but up to 18 can be spaced around the band. Two or more of the piezoelectric sensors can be provided in a single chest band. The various sensors are connected by cabling and accordingly the apparatus as a whole is quite bulky. Also, the data from the sensors is transferred to a remote location by wire via a connector. While the possibility of a radio link is mentioned, there is no detail as to how this would be achieved cost effectively to allow for disposability and yet ensure accurate and efficient data transfer from the various sensors.
International patent specification WO 94/01039 discloses physiological monitoring apparatus having a strip assembly for attachment to a patient""s chest. The strip comprises a series of nine electrically conductive electrode sensors for attachment to the precordial region of a patient""s chest for obtaining ECG data The strip only measures ECG data which is wirelessly transmitted on a multiplexed analog signal which modulates an RF carrier signal for transmission to a remote data analysis station which can be up to 50 to 100 meters from the strip. The emphasis here is to provide a complete ECG study of a patient using a portable system, and accordingly, there is no discussion of disposability and efficient communication of data from different types of sensors other than ECG.
An object of the invention is to avoid or at least mitigate the problems of the prior art. In particular, the invention seeks to provide an improved physiological sensor device which enables accurate and or continuous collection of various types of physiological data using a relatively inexpensive electrical system which can viably be disposed of after a single use over a 24 hour period. A further object of the invention is to provide a device which is able to collect a variety of types of physiological data, such as ECG, respiration, motion and/or temperature for example, while still being relatively inexpensive to manufacture. A yet further object is to use a single sensor for acquiring more than one type of physiological data.
Accordingly, a first aspect of the invention provides a portable and disposable physiological sensor device for attachment to a mammalian subject comprising physiological sensors for sensing the subject""s physiological parameters, such as ECG or respiration, and a controller operably in communication with the physiological sensor for communicating a signal representative of the sensed physiological parameter to an output which operably transmits the signal to a remote location.
Preferably, at least two physiological sensors are provided, each for sensing different ones of the subject""s physiological parameters. The controller is operably in communication with the physiological sensors so as to communicate a signal comprising data representative of both the sensed physiological parameters to an output transmitter which operably transmits the signal to a remote location. Preferably, the controller interleaves the data from both the physiological sensors into a serial output signal.
In a preferred embodiment, the controller of the invention comprises an application specific integrated circuit, and control circuits which are designed to have components communicate the signals between the sensor and output. Preferably, the output enables wireless transmission of the signal to a remote location, for example, using a digitally modulated electromagnetic carrier frequency such as a low frequency RF carrier for inductive coupling with a receiver. Also, the controller samples an analog signal from the physiological sensor and converts the sampled signal into a digital signal using an analog to digital converter.
Alternatively, a first and second respiration sensor may be provided, one of which preferably comprises a bend sensor locatable, for example, on the subject""s chest and preferably over or adjacent the subject""s pectoral muscle.
In accordance with the invention, the output preferably transmits a transmission signal comprising a data signal from two or more physiological sensors. Beneficially, the rate of transmission of the different signals from the two physiological sensors can be varied. Preferably, a first physiological sensor operably detects ECG data and the controller operably communicates a signal representative of the ECG data to the output transmitter at a first sampling frequency, and a second physiological sensor operably detects at least one of respiration, motion, and temperature data and operably communicates a signal representative of that data at a second sampling frequency to the output transmitter. Preferably, the first sampling frequency is as large as or greater than the second sampling frequency and, more preferably, approximately ten times greater than the second sampling frequency. For example, the first sampling frequency might be 250 Hz while the second sampling frequency might be 25 Hz.
According to another aspect of the invention, a disposable physiological sensor device for attachment to a mammalian subject is provided which is adapted for continuous use over a 24, or indeed longer, say 48, hour period, comprising a physiological sensor, a controller operably in communication with the physiological sensor which controller generates a signal representative of the subject""s physiological parameters such as ECG or respiration, and an output for transmitting the signal to a remote location. Accordingly, the device is generally disposable after a single continuous use. Beneficially, two or more physiological sensors are provided on the device.
According to a further aspect of the invention, a physiological sensor device for attachment to a mammalian subject is provided comprising a bend sensor which comprises an elongate member and an electrical component mounted thereon which electrical component has an electrical property which varies in dependence on the extent of bending of the elongate member, and an electrical monitoring device for detecting variation in the electrical property of the electrical component thereby to determine a physiological parameter such as respiration, of a subject in use. Preferably, the electrical component comprises an elongate resistor superimposed on the elongate member. The resistor can comprise a track of conductive ink and a series of two or more areas of highly conductive material such as metallic material over the conductive ink, thereby to effect a series of individual conductive sensors having a combined resistance less than the track of conductive ink without the areas of highly conductive material. Preferably, the elongate resistor or track of conductive ink, is substantially U-shaped. The elongate member can comprise a flexible substrate such as MYLAR(trademark). The device of the invention is preferably adapted to attach to a human chest for example over or adjacent the pectoral muscle of a subject and more preferably between a precordial position and the axilla of the subject in use, thereby to enable monitoring of the subject""s respiration, for example.
A further aspect of the invention provides a physiological sensor device comprising two electrode sensors operably locatable on a patient, a current generator for driving a current to each of the electrode sensors, and an impedance measuring device for determining variation in the impedance of the electrode sensors when attached to the subject in use thereby to determine a variation in the motion of the subject in use due to variation in the impedance at the electrical sensors caused by such motion. Preferably, the current generator comprises a sine wave generator which operably independently drives each of the two electrode sensors. The impedance measuring device can comprise a differential amplifier having an input from each of the two electrode sensors. The output signal from the differential amplifier can pass through a filter and demodulator before being AC coupled to a further stage of amplification. Preferably, the current generator generates an alternating current and the impedance measuring device comprises an anti-aliasing device after the further stage of amplification to ensure proper detection of the impedance signal. Preferably, the two electrode sensors are drive electrodes in a four electrode sensor arrangement for monitoring subject respiration.
A yet further aspect of the invention provides a portable physiological sensor device comprising a plurality of electrode sensors for use in measuring electrocardiographic data and respiratory data of a subject, wherein at least one of the electrode sensors is used in both the electrocardiographic and respiratory measurements, and an output transmitter responsive to outputs of the electrodes sensors so as to enable wireless transmission of the electrocardiographic data and respiratory data to a remote location. Preferably, the signal from at least one electrode sensor is sampled periodically by an ECG measuring device at a first sampling frequency and periodically at a second sampling frequency by a respiration measuring device. Preferably, the first sampling frequency is greater than the second sampling frequency. In a preferred embodiment the first sampling frequency is approximately ten times greater than the second sampling frequency and, for example, can be 250 Hz compared to a second sampling frequency of 25 Hz.
A further aspect of the invention provides a physiological sensor device attachable to a mammalian subject in use and comprising two electrode sensors adapted to assist in monitoring one of electrocardiographic data, and respiratory data of the subject and further comprising a motion detector which operably monitors the variation in impedance between the two electrode sensors thereby to determine the extent of motion of the patient in use. Preferably, the device comprises a first respiration sensor having the two electrode sensors and two further electrode sensors, wherein one pair of the two electrode sensors and the two further electrode sensors forms a pair of drive electrodes to which drive current is operably applied, and the other pair of the two electrode sensors and the further electrode sensors forms a pair of input electrodes to the respiration sensor. Preferably, the first respiration sensor comprises a differential amplifier having an input from each of the input electrodes. Also, the device preferably comprises a second respiration sensor having, for example, a bend sensor. The device can further comprise a temperature sensor.
Another aspect of the invention provides a physiological sensor device for attachment to a mammalian subject comprising a sensor for acquiring physiological data about the subject in use, and an output transmitter which receives a signal representative of the physiological data from the sensor and transmits the signal to a remote location, wherein the output transmitter comprises an inductive element for inductively coupling the output transmitter to a remote receiver at the remote location. Beneficially the inductive coupling enables efficient low powered transfer of data from the device.
Preferably, the output transmitter comprises a reservoir capacitor and the inductive element, which together improve the power efficiency of transmission. Also, the inductive element preferably has first and second ends each of which ends is connected via one of a pair of switches to the supply lines within the output transmitter to enable a reversing of the polarity across the inductive element. Preferably, the inductive element comprises a coil which forms part of an and after xe2x80x9cH-bridgexe2x80x9d circuit in the output transmitter. In a preferred embodiment the inductive element comprises a rectangular, substantially flat coil.
A yet further aspect of the invention provides a physiological sensor device for attachment to a mammalian subject, having one or more physiological sensors, an output for transmitting a signal from the one or more physiological sensors to a remote location, and a memory for storing a serial number for identifying the physiological sensor device which serial number is transmittable by the output with the signal. The serial number may be randomly generated. The device may comprise a random number generator and a controller for selecting a randomly generated number from the random number generator and storing the selected randomly generated number as the device serial number in the memory.
Beneficially, each of the physiological sensors according to any aspect of the invention can comprise any one or more of the following: a first stage of amplification, possibly including a variable amplifier stage; a filter, for example, a band pass filter, and a demodulation stage to remove any carrier frequency. A further stage of amplification, again possibly including a variable amplifier stage, can be provided followed by an anti-aliasing stage and subsequent switched capacitor low pass filter stage before passing the signal through a controller including an ASIC and control circuits which drive signals from pre-selected sensors to an analog to digital converter which in turn can be fed to the output where the digital signal can be used to modulate a pre-selected carrier frequency.